On the causes of evolutionary transition:transversion bias

Arlin Stoltzfus; Ryan W. Norris

Here we focus on whether direct measurements of fitness support the conservative transitions hypothesis, based on a collection of 8 studies comprising measured fitness values for 544 transitions and 695 transversions that change an amino acid. We assess the power of each study by comparing mutant fitnesses for each type of replacement (e.g., Ser to Pro) with a cross-validation predictor and with 2 existing measures of amino acid exchangeability called EX (Yampolsky and Stoltzfus 2005) and U (Tang, et al. 2004 ). We find that, for every mutation study, even the smallest, there is a significant correlation with one or more of these predictors; half of the studies show a highly significant correlation (P < 0.001). More importantly, for most studies, measured fitness values correlate significantly with a conservative-vs-radical distinction based on EX or U. Specifically, a replacement designated as "conservative" has a 65 % (EX) or 64 % (U) chance of being more fit than a "radical" replacement.